fix: Bitget WS keepalive — send text ping, not WebSocket PingMessage

Bitget v2 WS requires a text message "ping" every 30s, not a WebSocket
PingMessage control frame (opcode 0x9). Using the wrong ping type caused
a silent failure: connection stays up and subscription succeeds, but NO
ticker data is pushed — zero errors, zero reconnection logs.

Changes:
- connector.go: Add TextPing bool flag, send text 'ping' when set
- bitget.go: Set TextPing=true, handle text 'pong', add debug logging
- scanner.go: Expand to 179 overlapping Bitget+HL coins

exchange/bitget.go

@@ -47,30 +47,58 @@ func (b *BitgetWS) Run(updateFn func(coin string, price, bid, ask float64)) erro
 
 	b.Conn = NewPriceConnector(url, "Bitget", 120*time.Second, 30*time.Second)
 	b.Conn.PingInterval = 25 * time.Second // Bitget requires ping within 30s
+	b.Conn.TextPing = true                 // Bitget v2 expects text "ping" message
 
 	b.Conn.OnConnect = func() {
-		log.Printf("[Bitget WS] Connected, subscribing")
+		log.Printf("[Bitget WS] Connected, subscribing (%d symbols)", len(b.Tracked))
 
-		args := make([]map[string]string, 0, len(b.Tracked))
-		for _, sym := range b.Tracked {
-			args = append(args, map[string]string{
-				"instType": "USDT-FUTURES",
-				"channel":  "ticker",
-				"instId":   sym,
-			})
-		}
-		sub := map[string]interface{}{
-			"op":   "subscribe",
-			"args": args,
-		}
-		if err := b.Conn.SendJSON(sub); err != nil {
-			log.Printf("[Bitget WS] Subscribe error: %v", err)
+		// Batch subscriptions — Bitget WS has a limit per message
+		batchSize := 20
+		for i := 0; i < len(b.Tracked); i += batchSize {
+			end := i + batchSize
+			if end > len(b.Tracked) {
+				end = len(b.Tracked)
+			}
+			batch := b.Tracked[i:end]
+			args := make([]map[string]string, len(batch))
+			for j, sym := range batch {
+				args[j] = map[string]string{
+					"instType": "USDT-FUTURES",
+					"channel":  "ticker",
+					"instId":   sym,
+				}
+			}
+			sub := map[string]interface{}{
+				"op":   "subscribe",
+				"args": args,
+			}
+			if err := b.Conn.SendJSON(sub); err != nil {
+				log.Printf("[Bitget WS] Subscribe error (batch %d): %v", i/batchSize, err)
+			}
 		}
 	}
 
 	b.Conn.OnMessage = func(msg []byte) {
+		// Handle Bitget text "pong" response
+		if string(msg) == "pong" {
+			return
+		}
+
+		// Check for Bitget subscription confirmation or error response
+		var generic map[string]interface{}
+		if err := json.Unmarshal(msg, &generic); err == nil {
+			if evt, _ := generic["event"].(string); evt == "error" {
+				log.Printf("[Bitget WS] Subscribe error response: %s", string(msg))
+				return
+			} else if evt == "subscribe" {
+				log.Printf("[Bitget WS] Subscribe confirmed: %s", string(msg))
+				return
+			}
+		}
+
 		var ticker bitgetTickerMsg
 		if err := json.Unmarshal(msg, &ticker); err != nil {
+			log.Printf("[Bitget WS] Unrecognized message: %s", string(msg))
 			return
 		}
 		if len(ticker.Data) == 0 || ticker.Data[0].LastPr == "" {